Boeing Acknowledges Tests Underestimated 787 Battery Risks

By MATTHEW L. WALD and JAD MOUAWAD

April 23, 2013

WASHINGTON — Boeing acknowledged on Tuesday that its original tests of the lithium-ion batteries on its 787 planes underestimated the risks of fire, though it defended its previous assessment that such a hazard was extremely unlikely.

At the start of a two-day hearing held by the National Transportation Safety Board, Boeing’s chief engineer on the 787, Mike Sinnett, said the calculation that a battery would fail only once every 10 million flight hours applied to the design of the battery and did not include possible manufacturing flaws. The testimony seemed to point to GS Yuasa, the Japanese manufacturer of the battery.

The purpose of the safety board’s hearing was to determine how Boeing and the Federal Aviation Administration — despite years of careful work — could have missed the potential for catastrophic failure when the battery was initially certified in 2007. But the broader focus was how the plane’s manufacturers and regulators can cope with rapid changes in technology that may outstrip their ability to predict problems. The 787 is the first major commercial airplane to make extensive use of lithium-ion batteries.

The safety board is investigating the fire on Jan. 7 in a Japan Airlines 787 parked at a gate at Boston’s Logan Airport. A second incident, involving a similar battery on an All Nippon Airways plane on a Japanese domestic flight, led to the grounding of all 50 of the planes Boeing has so far delivered.

“We are here to understand why the 787 experienced unexpected battery failures following a design program led by one of the world’s leading manufacturers and a certification process that is well-respected throughout the international aviation community,” Deborah A. P. Hersman, the board’s chairwoman, said.

Mr. Sinnett said the failure calculation was based on data provided by GS Yuasa. “That value essentially is reached by experience with similar type cells,” he said. “GS Yuasa had experience with over 14,000 cells of similar makeup. They had millions upon millions of those cells without any cell venting.”

One of the tests consisted of driving a nail into a battery cell to provoke a short circuit. While the cell failed, the test did not result in a fire. But under repeated questioning, Mr. Sinnett acknowledged that the nail test had been inadequate and was not “conservative enough.” Boeing, he said, found that the batteries could catch fire only if they were overcharged.

The Boeing executive was pressed to say whether the company stood by its original risk estimate. He declined to do that until investigators could determine the cause of the two battery failures. Ms. Hersman did not seem satisfied with the answer. At one point she said, “There is some obfuscation here.”

During questioning, Mr. Sinnett gave a narrower definition of Boeing’s risk estimate than the company had in the past. “That once in 10 million flight hours doesn’t apply to things like abuse of the battery,” he said. “It doesn’t necessarily apply to a nonconforming battery, meaning a battery that was not built for the type design. So there are other things that can cause the failure of a battery that don’t contribute to that one in 10 million hours.”

Later in the day, representatives of GS Yuasa responded by describing their intensive testing of the batteries and their long experience in making similar cells.

Boeing used a large number of subcontractors for the 787s. It picked a French company, Thales, to provide the 787’s power conversion system. Thales, in turn, chose GS Yuasa to build the lithium-ion batteries for the planes. But a GS Yuasa executive made clear during the hearing that both Boeing and Thales were involved in all of its testing and design phases.

“GS Yuasa provided designs, and Thales and Boeing reviewed them and sometimes made suggestions and approved them,” said Takahiro Shizuki, the manager of large-scale batteries at GS Yuasa.

The F.A.A. last week approved Boeing’s plans to fix the plane’s lithium-ion batteries, an important step in lifting the grounding of the 787s in the United States. After the grounding of the fleet, Boeing made several changes to its original battery design. These fixes include adding better insulation between the batteries’ eight cells and building a stainless steel box that will encase the batteries and contain any fire and vent possible smoke or hazardous gases out of the planes.

“There is still more work to be done in the investigation,” Ms. Hersman said.

Boeing told the F.A.A. it planned to use lithium-ion batteries on its 787 in 2003. Because airplane regulations at the time did not cover such batteries, the F.A.A. in 2007 approved Boeing’s use under nine special conditions that covered the need to contain or vent any hazardous materials.

Mr. Sinnett defended the plane maker’s choice of lithium-ion batteries, saying at the hearing that the 787’s certification by regulators took 200,000 hours and was the most “extensive in our company’s history.” He added that the battery’s certification was “very rigorous and subject to close scrutiny by the F.A.A.”

Yet the fire in Boston also showed something that the regulators and the company did not expect: that a flaw, possibly no larger than a grain of sand, in a single cell could set off a chain reaction that would cause smoke or fire in adjacent cells.

“We were focused on the hazards of the battery,” said Ali Bahrami, a senior F.A.A. official in charge of the 787 certification. “We knew the hazards were always there. The awareness was always there. We did the best we could under the circumstances, and the knowledge that existed then, to come up with standards that address the requirements for this particular battery.”

Steve Boyd, another F.A.A. senior official, said: “You have to look at the special conditions as a comprehensive and mutually supportive requirement intended not only to reduce the probability of a thermal event but to mitigate the effects of any of those failures if they occur.”

It is the second public hearing by the safety board on lithium batteries. On April 11 and 12, the board held a two-day forum focused mostly on the batteries as cargo and components in devices carried by passengers.